Why not?
Most companies that end up with that kind of hardcore legacy code a) refuse to upgrade on a reasonable basis and b) refuse to compensate their developers in proportion to the value they ultimately deliver.
So, fuck'em. Might as well enjoy the pseudo pension.
If the company has pidgeon holed themselves into the situation, they clearly have the 2 options you stated, and that should not reflect poorly on the original author.
There's a good chance, from my understanding of the situation, that his managers don't understand the situation as well as he does. I think he should think bigger than himself.
Management's decisions are unlikely to be budget related.